This application claims the benefit of Korean Patent Application No. 10-2004-0107214, filed on Dec. 16, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a catayst used in producing polycarbonate from an epoxy compound and carbon dioxide and a method of producing polycarbonate using the catalyst, and more particularly, to a bimetallic coordinating compound in which ligands coordinated to two metal atoms are linked via a spacer, the bimetallic coordinating compound being used in producing polycarbonate, and a method of producing polycarbonate using the compound.
2. Description of the Related Art
Polycarbonates are easily biodegradable and useful as, for example, packages or coating materials. Since 1960s, many researchers have developed various types of catalysts used in producing polycarbonate from an epoxy compound and carbon dioxide and most of the developed catalysts are metallic zinc compounds.
The methods of producing polycarbonate from an epoxy compound and carbon dioxide are very environment-friendly since phosgene, a toxic compound, is not required and carbon dioxide can be obtained from the air.
Inoue, S. et al. reported a method of producing polycarbonate using a non-uniform catalyst obtained by partially hydrolyzing a zinc diethyl compound (J. Poly. Sci. Lett. B7, 287-292 (1969)). However, the catalyst has a very low activity.
Aida, T. et al. reported a method of producing polycarbonate using an aluminum porpyrin catalyst (J. Am. Chem. Soc. 105, 1304-1309 (1983)). This catalyst has a turnover rate of 0.3 turnover/hr or less, i.e., has a low activity.
D. J. Darensbourg described an improved method of producing polycarbonate using a well-defined zinc complex and obtained a turnover rate of 2.4 turnover/h (Macromolecules, 28, 7577-7579 (1995)). M. Super et al., described other improved method of producing polycarbonate using a catalyst compound obtained from zinc oxide, of which chemical structure is not clearly defined, and obtained a turnover rate of 8.4 turnover/hr (Macromolecules, 30, 368-372 (1997)). However, since the activities of these catalysts are low, the catalysts cannot be used. When these catalysts are used, phenoxy composing ligands of the catalysts are introduced into ends of the polymer chains.
Coates, G. W. et al. developed a highly active catalyst by using a zinc complex comprising β-diketiminate ligand (U.S. Pat. No. 6,133,402). According to the substituent of the β-diketiminate ligand, a maximum turnover rate of 1,116 turnover/hr can be obtained. The research group of Coates, G. W. obtained a maximum turnover rate of 2,300 turnover/hr using a zinc catalyst having a similar structure (J. Am. Chem. Soc. 125, 11911-11924 (2003)).
In addition, methods using chromium-based catalysts were reported (Kruper, W. J. et al., J. Org. Chem. 60, 725-727 (1995), Mang, S. et al., Macromolecules, 33, 303-308 (2000), Stamp, L. M. et al., Chem. Commun. 2001, 2502-2503, Darensbourg, D. J. et al., J. Am. Chem. Soc. 124, 6335-6342 (2002)). In these methods, catalytic activities are lower than the zinc catalysts.
According to the research results of the research group of Coates, G. W. (J. Am. Chem. Soc. 125, 11911-11924 (2003)), for the zinc complexes comprising β-diketiminate ligand to catalyze the production of polycarbonate from an epoxy compound and carbon dioxide, a cooperative operation of two zinc complexes is required. To ensure that the cooperative operation occurs according to the reaction mechanism, a distance between zinc-zinc atoms should be maintained appropriate for the polymerization reaction.
That is, when bulkiness of the substituent of β-diketiminate ligand is too low and the distance between zinc-zinc atoms is too short, an interaction between two zinc coordinate compounds is too strong. Thus, the polymerization does not proceed. Contrary to this, when bulkiness of the substituent of β-diketiminate ligand is too high and the distance between zinc-zinc atoms is too long, a monomer coordinated to one zinc atom cannot be easily transferred to a polymer chain coordinated to the other zinc atom, and thus a rate of the polymerization reaction is low. Thus, in this method, the catalytic activity was maximized by controlling the bulkiness of the substituent to maintain the appropriate distance between zinc-zinc atoms. However, since a probability that the cooperative operation of the two zinc complexes occurs during the polymerization reaction is too low when the concentration of the catalyst in a polymerization reaction system is too low, a very low ratio of monomer/catalyst must be maintained. For this reason, they suggested in U.S. Pat. No. 6,133,402 that a ratio of monomer/catalyst be limited to 100-4,000. Accordingly, the method is not suitable for producing a polymer having a high molecular weight. In the method, a maximum turnover per catalyst molecule is about 1,116 and a number average molecular weight of the resultant polymer is 5,000-40,000.